Your body contains potassium and carbon, and a tiny fraction of those atoms are radioactive (potassium-40 and carbon-14). In an adult, several thousand of them decay every second. It's harmless, part of the natural radiation every living thing has always lived with. Fun side effect: sleeping next to someone gives you a minuscule dose of their radioactivity.
Cooled below −183 °C, oxygen turns into a pale blue liquid. Pour it between the poles of a strong magnet and, instead of flowing away, it hangs suspended between them. The reason lies in its unpaired electrons, which respond to the magnetic field. Liquid nitrogen, by contrast, is colourless and pours straight through.
In 2012, Felix Baumgartner jumped from a capsule hanging beneath a balloon, about 39 kilometres up. In that extremely thin air almost nothing slowed him down, and he reached around 1,358 km/h in free fall, or Mach 1.25. He became the first person to exceed the speed of sound with nothing but his own body.